1. Field of the Invention
The present invention relates to a polygon mirror and an optical scanning apparatus employing the same. More particularly, the present invention relates to a polygon mirror that is capable of withstanding a tensile load generated due to a rotational force during high speed rotation, and an optical scanning apparatus employing the same.
2. Description of the Related Art
An optical scanning apparatus, which is commonly employed with an image recording apparatus that prints an image on a sheet of printing paper, such as a copier, printer, facsimile or the like, forms an electrostatic latent image by scanning light beams emitted from a light source, such as a laser diode, onto a photosensitive medium of the image forming apparatus.
FIG. 1 is a perspective view of a general polygon mirror for use in an optical scanning apparatus. Referring to FIG. 1, a polygon mirror 10 includes a mirror body 11 having a plurality of square mirror surfaces 12, and is used as an optical deflector that deflects a light beam to the optical scanning apparatus. The polygon mirror 10 rotates at a constant speed by means of a driver, such as a motor (not shown), during an image forming operation.
The optical scanning apparatus scans the light beam on a scan surface in a scanning direction by rotating the polygon mirror 10, thereby recording an image on a photosensitive drum (not shown).
The polygon mirror 10 is a processed product having sub-micron level precision and reflectivity. Accordingly, control of a manufacturing process of the polygon mirror 10 is quite difficult to achieve and the use of high-purity aluminum makes the process require an extended processing time, resulting in a high manufacturing cost and capital investment for facilities, and difficulties in supplying quantities to meet demands. To overcome such problems, research into methods of manufacturing a polygon mirror by molding the polygon mirror by plastic molding, pressing, or die casting, and performing mirror surface coating on the polygon mirror, has been continuously conducted.
In the case of plastic molding, a deformation due to shrinkage exhibited after the plastic molding makes surface precision of the polygon mirror unsatisfactory. Another approach has been proposed to maintain the configuration of a polygon mirror even with the shrinkage of plastic materials such that a plastic material is mixed with spherical ceramic particles and then molded, as disclosed in Japanese Patent Laid-open Publication No. 01-113718, the entire disclosure of which is hereby incorporated by reference.
However, the use of spherical ceramic particles makes it impossible to withstand a tensile load due to a rotational force exerted during high-speed rotation of approximately 40,000 rpm or higher, even though the dimensional and configuration accuracy requirements can be satisfied. In this case, the polymer material, which mostly serves as a binder, must withstand the tensile load. However, the tensile strength of the polymer material is too low to withstand the tensile load due to a rotational force, thus limiting the application of the polygon mirror on the basis of rotation speed, that is, limiting the application of the polygon mirror to rotation speeds of not greater than 20,000 rpm.
Accordingly, a need exists for a polygon mirror having a durability that is high enough to withstand a tensile load due to a rotational force exerted during high-speed rotation.